Preventing silica bake-on deposits from silicate detergent composition



1 S3 REFERENCE United States Patent 0 3 436,350 PREVENTING SILlCA BAKE-0N DEPOSITS FROM SILICATE DETERGENT COMPOSITION Donald J. Schwedler, West Covina, Calif., assignor to forth a new detergent composition 3,436,350 Patented Apr. 1, 1969 containing a crystalline silicate and an amount of boric acid and/or a borate salt sufficient to form a calculated disilicate when the mixture is dissolved in water.

Clifiord E. Schitfer, doing business as Calusa Associates Other objects and advantages of the instant invention No Drawing. Filed Oct. 26, 1964, Ser. No. 406,544 will become more apparent from the following detailed Int. Cl. Clld 3/06, 3/08, 7/56 description and examples.

CL 252-135 4 Claims As stated above it has been found that these deposits This invention relates to a new detergent composition and a process for preventing the deposition of opaque deposits on articles washed therewith. More specifically, it

deals with silicated detergent compositions highly useful in automatic dishwasliing machines, whereby the deposispotted areas on the tidn of opaque films and dense white articles being washed is prevented.

Detergent compositions used in mechanical dishwashing machines usually comprise in combination an alkaline detergent salt, e.g., sodium metasilicate, an alkaline condensed phosphate, e.g., sodium tripolyphosphate, and an alkaline carbonate, e.g., sodium carbonate.

Clear transparent drinking glasses washed with the above described composition oftentimes exhibit an opaque film and dense white spotted areas where the detergent has baked onto the glass. Aluminum pots and pans also exhibit unsightly white streaks when washed in silicate containing detergents. It has been found that these deposits are caused by the the silicate present in the detergent. These silicates however are essential ingredients of alkaline detergent compositions because of their excellent on glasses and pots and pans, etc., washed with detergent compositions in automatic dishwashing machines are a result of the silicate contained in the detergent. In evaluating the bake-on characteristics of the alkaline detergent salts, the following procedure was used showing both their singular and blended efiect.

Procedure for evaluating detergent bake-on of solution to a clean 70 watch glass over an both into an oven mm. Pyrex watch glass. Place empty 250 ml. beaker and then place for minutes at 210 F. Allow to cool five minutes. Then rinse residue with a stream of distilled water from a 7 mm. Place Pyrex watch glass and minutes to dry.

The detergent salts or glass tubing for 30 seconds. beaker into the oven for 15 Examine for bake-on residue.

blends thereof in the aforementioned formula, were evaluated singly and in combination by the bake-on test,

the result of which are shown anticorrosive and detergent qualities. 3 in Table I.

TABLE I Detergent Salt Appearance A pearanee Before Rinsing After Rinsing Sodium tri lyphosphat White residue-.. Clear. Sodium car one ..d0 Do. Sodium metasilicate. anhydrous..- ....do White residue. 5 do. Clear. 8021111111 tripbplyp h 3. P

o ium car ona e, 20311111 I 0: gnigdrous, 22 pit-L. residue" 0 um 05D 5 9 Sodium me s-S cats, 22 y Sodium carbonate, 28 parts Sodium metasilicate, anhydrous, 22 parts- .do Do socium tripolyphosphate, 46 parts It is therefore an object of the instant invention to produce a silicated detergent composition which will not cause streaks, films or deposits on articles being washed therewith.

Another object of the instant invention is to set forth a process for preventing silicated detergent compositions from depositing films, streaks or spotted areas on the articles being washed.

A further object of the instant invention is to set forth a process of preventing silicate containing detergent compositions for dishwashing machines from depositing films, streaks, or spots on the articles being washed, by means of adding to the composition boric acid and/or its alkali metal salts in prescribed amounts.

A still further object of the instant invention is to set Sodium metasilicate (Nero-S101) admixed with boric acid tion 0.5257

From the above were is silicate cannot be easily rinsed apparent that sodium metafrom glass after bake-on.

The Na O/SiO, ratio of crystalline silicates extends from sodium orthosilicate (Na,O/SiO,=2/l) through sodium metasilicate (Na,O/Si0,=l/ 1) to colloidal sodium disilicate (Na;O/SiO;=1/2). Silicates of Na O/SiO, ra-

tios between 1/1 and 1/2 are actually mixtures of crystalline sodium metasilicate and colloidal sodium disilicate and will be considered part of this invention.

1 have discovered that the bake-on characteristics of crystalline silicates, when admixed with a calculated amount of boric acid and/or its alkali metals salts, will not only be altered but can The following examples were prepared and tested to determine the exact mole essary to prevent deposits.

be completely prevented.

ratios of borate to silicate nec- These are disclosed in Table 11.

TABLE II and various alkali metal borates. Total concentra- Mole ratio Appearance Boron Salt Nero/B20; metasilicate] alter rinsing boron salt Borlc acid, H;B0| 0/1 1/1 Clear. Potassium pentaborat/e, KIBGO1-3BIOI8H2 0.2/1 8/1 Do. Sodium tetraborate, NazB4O1-5H;O.-... 0. 6/1 l/1 Do. 'Do 0. 5/1 2/1 Do. Do 0. 5/1 3/1 Opaque White. Sodium metaborate, Marmot-SE10 1/1 2/1 Do. Do 1/1 l/l Do. Do 1/1 1/2 Do. Potassium tetraborate, KzB 0.5/1 2/1 Clear.

The mole ratios of boron containing compounds to silicate compounds were calculated in accordance with the following equations:

I have found that the boron salts listed in Table II and in Example I which includes the entire range from boric acid to metaborate (Na O/B O from /1 to 1/ 1) are equally efiective in preventing the undesirable silica bake-on of crystalline silicates over the complete Na O/SiO, span of 2/ 1 to 1/ 2.

Tests were also made of sodium orthosilicate (2Na,O-SiO having a Na,O/Si0 ratio of 2/1, sodium sesquisilicate (3 Na,Q-2Si0,- 11H,O) having a Na O/SiO, ratio of 3/2, and sodium silicate liquid (Na,O-16Si0,) having a Na,O /Si0 ratio of l/ 1.6 both alone and with boron salts listed in Table II. Without the boron salts these three silicates produced a difiicult to remove white silica bake-on.

When mixed with the boron salts in accordance with Equations 7 through 15, a clear appearance was produced after rinsing in the silica bake-on evaluation tests. Table 11 lists the various maximum silicate/boron ratios tested. Sodium metasilicate is shown for comparison.

TABLE III [Silicate/Boron Ratios] Sodium Sodium Sodium Liquid Orthosllicate Sesquisilicate Metasillcate Sodium Silicate Boric acid, H.130; 1/3 1/4 1/1 /2 Potassium pentaborste. K2B407-3B2058H20... 8/3 2/1 8/1 /1 Sodium tetraborate, NBZB407'5H2O 2/3 1/2 2/1 5/1 Potassium tetraborate, K2B401'4H2O 2/3 1/2 2/1 5/1 Sodium metaborate, Na1B1Oi-8H1O 1/3 1/4 1/1 6/2 1 For each mole of sodium metaborate used, a mole of sodium dihydrogen phosphate was jointly used.

metasilicate to sodium tetraborate produced an opaque white film, indicating that an insufiicient amount of borate salt was present to prevent silica bake-on.

As seen in Table II, sodium metaborate did not prevent the silica bake-on in any mole ratio tested. This can be remedied by acidifying the sodium metaborate with an acid salt and simultaneously blending with sodium metasilicate.

As shown in Equation 5, when two moles of sodium metaborate are acidified by two moles of monosodium dihydrogen phosphate, one mole of sodium tetraborate is formed. Therefore a mixture as shown in Example I below of two moles of sodium metaborate, two moles of sodium dihydrogen phosphate and two moles of sodium metasilicate did produce a clear appearance after rinsing in the silica bake-on evaluation test.

EXAMPLE I Moles Sodium metaborate (Na,B,O -8H;O) 2 Sodium dihydrogen phosphate (NaH PO -H 0) 2 Sodium metasilicate (Na OSiO 2 In order to show that the acid phosphate salt such as that used in Example I, did not in itself prevent silica bake-on, tests were made on a mixture of sodium metasilicate and sodium dihydrogen phosphate in the absence of boron salts in accordance with Equation 6 below. This mixture did not prevent a silica bake-on when tested in agtgordance with the silica bake-on evaluation test used a ve.

These acid phosphate salts (sodium dihydrogen phosphate, disodium phosphate and trisodium phosphate) were then tested alone and in admixture (1/1 mole mixture of disodium phosphate and trisodium phosphate). All produced a clear appearance when tested for bake-on in the absence of sodium metasilic te.

The equations used for preparing Table In are as follows:

(15) Na B O 5H O+5 (Na O 1 6SiO 4NaBO -I-4(Na O 25103) +5H O In all of the above tests only the sodium salt is illustrated. It is possible, however, to use any of the alkali metal salts. To further illustrate this the following tests were made with potassium borates in accordance with the same ratios as shown by Equations 1 through 6. These tests are illustrated in Table IV which shows that the potassium metasilicate also produces a white residue as does the sodium metasilicate and this silica bake-on or residue is prevented by the use of either potassium borate or sodium borate salts.

The following examples set forth detergent compositions containing the prescribed ratios of boron containing compounds. Example A is a detergent composition for soft water and Example B discloses a typical detergent composition for both soft and hard water.

Example A.--Soft water A detergent composition was prepared by blending for ten minutes in a ribbon mixer comprising by weight parts of anhydrous trisodium phosphate, 48.2 parts of sodium tetraborate 5 mole hydrate, and 36.8 parts of anhydrous sodium metasilicate. To the mixture of alkaline detergent salts was dispersed 3 parts of a liquid low foaming nonionic surfactant followed by 2 parts of an organic chlorine releasing chemical as potassium dichloroisocyanurate. The final mixture was evaluated for bake-on using a Pyrex watch glass and also an aluminum evaporating dish as commonly used in a commercial laboratory. No silica bake-on was observed on either glass or aluminum when the detergent mixture was evaluated in soft water. However, an opaque white residue was observed on both aluminum and glass when the detergent mixture was evaluated in hard water from the tap of 17.1 grains hardness calculated as CaCO It is apparent that the detergent composition of Example A is suitable for use in soft water but does not produce the desired result in hard water. This defect is easily overcome by using a water soluble phosphate, e.g., tripolyphosphate, or an organic sequestrant having sequestering capacity for the calcium and magnesium present in hard water. The method is described in the following example.

Example B.-Both soft and hard water A detergent composition was prepared by blending in a ribbon mixer comprising by weight 46 parts of sodium tripolyphosphate-light density to which 3 parts of a low foaming nonionic surfactant was dispersed, followed by 27 parts (0.0927 mole) of sodium tetraborate, 5 mole hydrate and 22 parts (0.1803 mole) of anhydrous sodium metasilicate. Finally, 2 parts of potassium dichloroisocyanurate was added and the entire mixture made uniform by an additional 5 minutes blending. This particular composition produced a clear appearance on both glass and aluminum in both soft and hard water (17.1 grains) when evaluated by the silica bake-on test. The mole ratio of sodium metasilicate to sodium tetraborate is 1.94/1, since a slight excess of the latter is present.

A liquid composition was prepared containing only potassium salts according to the following equations:

The ingredients were added and mixed with an agitator in the order shown.

Parts by weight Soft water Y 27.5 Tetra potassium pyrophosphate 22.5 Liquid caustic potash (50%) 12.55 Liquid potassium silicate (27.3%)

(KgO/SlOg=1/2.5) 23.2 Potassium tetraborate (KQB4074H30) 14.25

A clear liquid resulted and when tested at 1.05% concentration on glass and aluminum by bake-on test, a clear appearance resulted.

It is apparent from the foregoing that there is provided a new detergent composition which will not cause streaks, films or deposits on articles washed therewith and a process for preventing such undesirable characteristics in silicate containing detergents, by means of including in or adding to such detergent compositions boric acid or alkali metal borates in sufficient amount to form a calcualted disilicate when the mixture is dissolved in water. It is further apparent from the above that the boron containing compound may be any compound having a Nap/B 0 range of 0/ 1 to 1/1. It is also possible for the composition to be used as a steam cleaning compound.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invenion is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

I claim:

1. A method of preventing silica bake-on deposits from mechanical dishwashing machine detergents containing alkali metal silicates wherein the silicates are selected from the group consisting of orthosilicate, sesquisilicate, metasilicate and silicate liquid consisting essentally of, adding to said detergents a boron containing compound selected from the group consisting of boric acid and alkali metal borates in at least a stoichiometric amount sufiicient to convert the crystalline silicate to the disilicate when the mixture is dissolved in water.

2. The method of claim 1, wherein the silicate in the detergent composition has a Nap/S10, ratio in the range of 2/1 to 1/2 and the boron containing compound is a sodium borate in the Nap/B 0 range of 0/1 to 0.5/1.

3. The method of claim 1, wherein the boron containing compound ins an alkali metal metaborate and sufficient acid phosphate salt selected from the group consisting of sodium dihydrogen phosphate and disodium phosphate is added to convert the metaborate to a Nap/B 0 ratio in the range of 0/1 to 0.5/ 1.

4. A method of preventing silica bake-on deposits from mechanical dishwashing machine detergents comprising using a dishwashing composition consisting essentially of from 10-46 parts of a phosphate selected from the group consisting of sodium dihydrogen phosphate, disodium phosphate, trisodium phosphate and sodium tripolyphosphate, 22-368 parts of an alkali metal silicate selected from the group consisting of orthosilicate, sesquisilicate, metasilicate and silicate liquid and from 27-482 parts of a boron containing compound selected from the group consisting of boric acid and alkali metal borates, all of said parts being by weight of the composition.

References Cited UNITED STATES PATENTS 2,502,881 4/1950 Parker 252109 2,673,841 3/1954 Reinhard 252 X 2,867,585 1/1959 Vitale 252135 3,128,250 4/1964 Lintner 252135 X 3,001,945 9/1961 Drew et al. 252137 3,157,649 11/1964 Symes 25299 LEON D. ROSDOL, Primary Examiner. B. BETTIS, Assistant Examiner.

U.S. Cl. X.R.

g gs UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 3 ,35 Dated April 9 9 DONALD J. SCHWEDLER Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column '9, line 5, TABLE IV should read:

TABLE IV Detergent Salt S1lica Bake-on Result Potassium metasilicate (K O.SiO 2 moles a earance Potassium tetraborate (K Buo'p lfi O) 1 mole pp Potassium metasilicate 30.810 2 moles Sodium tetraborate (Na Bq .515% 1 mole Potassium metasilicate (K O.SiO --White residue;

SIGNED AND SEALED MAR 241970 (SEAL) Attest:

Edward 1V1. Fletcher, 11'. WILLIAM E sum) 1m R :fiiqsting Officer Commissioner of Patents 

4. A METHOD OF PREVENTING SILICA BAKE-ON DEPOSITS FROM MECHANICAL DISHWASHING MACHINE DETEGENTS COMPRISING USING A DISHWASHING COMPOSITION CONSISTING ESSENTIALLY OF FROM 10-16 PARTS OF A PHOSPAHATE SELECTED FROM THE GROUP CONSISTING OF SODIUM DIHYDROGEN PHOSPHATE, DISODIUM PHOSPHATE, TRISODIUM PHOSPHATE AND SODIUM TRIPOLYPHOSPHATE, 22-36.8 PARTS OF AN ALKALI METAL SILICATE SELECTED FROM THE GROUP CONSISTING OF ORTHOSILICATE, SESQUISILICATE, METASILICATE AND SILICATE LIQUID AND FROM 27-48.2 PARTS OF A BORON CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF BORIC ACID AND ALKALI METAL BORATES, ALL OF SAID PARTS BEING WEIGHT OF THE COMPOSITION. 